Catalyst, its preparation and use

ABSTRACT

A dehydrogenation catalyst is described that comprises an iron oxide, an alkali metal or compound thereof, and rhenium or a compound thereof. A process for preparing a dehydrogenation catalyst comprising preparing a mixture of iron oxide, an alkali metal or compound thereof, and rhenium or a compound thereof is also described. Additionally, a dehydrogenation process using the catalyst and a process for preparing polymers are described.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 60/915,808 filed May 3, 2007, the entire disclosure of which isherein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a catalyst, a process for preparing thecatalyst, and a process for the dehydrogenation of a dehydrogenatablehydrocarbon.

BACKGROUND

Dehydrogenation catalysts and the preparation of such catalysts areknown in the art. Iron oxide based catalysts are customarily used in thedehydrogenation of dehydrogenatable hydrocarbons to yield, among othercompounds, a corresponding dehydrogenated hydrocarbon. In this field ofcatalytic dehydrogenation of dehydrogenatable hydrocarbons todehydrogenated hydrocarbons there are ongoing efforts to developdehydrogenation catalysts that exhibit improved performance.

U.S. Pat. No. 6,191,065 describes a catalyst for the production ofalkenylaromatics from alkylaromatics, wherein the catalyst ispredominantly iron oxide, an alkali metal compound and less than about300 ppm of a source for a noble metal, such as palladium, platinum,ruthenium, rhenium, osmium, rhodium or iridium. The amount of noblemetal may be as much as 1000 ppm although the preferred amounts arelower. The patent teaches that when the noble metal is palladium,rhenium and rhodium, the amount is preferably less than 100 ppm, andmost preferably less than 20 ppm. The catalyst may also comprisecompounds based on cerium, molybdenum, tungsten and other suchpromoters.

SUMMARY OF THE INVENTION

The present invention provides a dehydrogenation catalyst comprising aniron oxide, an alkali metal or compound thereof, and rhenium or acompound thereof.

In a preferred embodiment, the invention provides a dehydrogenationcatalyst comprising iron oxide, an alkali metal or compound thereof, andrhenium or a compound thereof wherein the rhenium or compound thereof ispresent in an amount of at least about 0.01 moles of rhenium per mole ofiron oxide, calculated as Fe₂O₃.

The present invention provides a process for preparing a dehydrogenationcatalyst comprising preparing a mixture of an iron oxide, an alkalimetal or compound thereof, and rhenium or a compound thereof wherein therhenium is present in an amount of at least about 0.01 moles of rheniumper mole of iron oxide, calculated as Fe₂O₃ and calcining the mixture.

The present invention also provides a process for preparing adehydrogenation catalyst comprising preparing a mixture of iron oxide,an alkali metal or compound thereof, and a rhenium compound selectedfrom the group consisting of rhenium dioxide, rhenium trioxide,rhenium(VII) oxide, and ammonium perrhenate and calcining the mixture.

The present invention further provides a process for dehydrogenating adehydrogenatable hydrocarbon comprising contacting a feed comprising adehydrogenatable hydrocarbon with a catalyst comprising an iron oxide,an alkali metal or compound thereof, and rhenium or a compound thereof.

The present invention still further provides a method of using adehydrogenated hydrocarbon for making polymers or copolymers, comprisingpolymerizing the dehydrogenated hydrocarbon to form a polymer orcopolymer comprising monomer units derived from the dehydrogenatedhydrocarbon, wherein the dehydrogenated hydrocarbon has been prepared ina process for the dehydrogenation of a dehydrogenatable hydrocarbon asdescribed above.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a catalyst that satisfies the need forimproved dehydrogenation catalysts. The catalyst comprises an ironoxide, an alkali metal or compound thereof, and rhenium or a compoundthereof. The catalyst comprising rhenium is more selective than asimilar catalyst that does not contain rhenium. Additionally, a catalystcomprising rhenium and silver demonstrates improved performance over asimilar catalyst that does not contain rhenium and silver.

The dehydrogenation catalyst is an iron oxide based catalyst. Inaddition, the iron may be present in the form of potassium ferrite or asa compound with any of the other catalyst components including rhenium.The catalyst comprises from 10 to 90 wt % iron oxide, calculated asFe₂O₃. The catalyst preferably comprises from 40 to 85 wt % iron oxide,and more preferably comprises from 60 to 80 wt % iron oxide.

The iron oxide may be formed or processed by any process known to thoseskilled in the art. Additionally, the catalyst may comprise one or moretypes of iron oxide. The iron oxide may be formed by heat decompositionof iron halide to form iron oxide as described in U.S. PatentApplication Publication 2003/0144566, which is hereinafter referred toas regenerator iron oxide. The regenerator iron oxide may optionally betreated to reduce the residual halide content in the iron oxide to atmost 2000 ppm or preferably at most 1500 ppm. The iron oxide may beformed by spray roasting of iron chloride in the presence of Column 6metals or hydrolyzable metal chlorides. In the alternative, the ironoxide may be formed by a precipitation process.

The iron oxide may be restructured before its use in the catalyst by theprocess described in U.S. Pat. No. 5,668,075 and U.S. Pat. No.5,962,757. The iron oxide may be treated, washed or heat conditionedbefore its use in this catalyst as described in U.S. Pat. No. 5,401,485.

The iron oxide may be red, yellow, or black iron oxide. Yellow ironoxide is a hydrated iron oxide typically depicted as Fe₂O₃.H₂O orα-FeOOH. When yellow iron oxide is added, at least 5 wt %, or preferablyat least 10 wt % of the total iron oxide in the catalyst, calculated asFe₂O₃, may be yellow iron oxide, and at most 50 wt % of the total ironoxide may be yellow iron oxide. An example of a red iron oxide can bemade by calcination of a yellow iron oxide made by the Penniman method.Iron oxide-providing compounds that may be present in the catalystinclude goethite, hematite, magnetite, maghemite, and lepidocricite.

The alkali metal in the catalyst is selected from the group of alkalimetals including lithium, sodium, potassium, rubidium, cesium andfrancium, and is preferably potassium. One or more of these metals maybe used. The alkali metal may be present in the catalyst as a compoundof an alkali metal. The alkali metals are generally present in a totalquantity of at least 0.2 moles, preferably at least 0.25 moles, morepreferably at least 0.45 moles, and most preferably at least 0.55 moles,per mole of iron oxide, calculated as Fe₂O₃. The alkali metals aregenerally present in a quantity of at most 5 moles, or preferably atmost 1 mole, per mole of iron oxide. The alkali metal compound mayinclude hydroxides; carbonates; bicarbonates; carboxylates, for example,formates, acetates, oxalates and citrates; nitrates; and oxides. Thepreferred alkali metal compound is potassium carbonate.

The rhenium may be present as any compound of rhenium, and is preferablyrhenium oxide. The rhenium may be added as any compound of rhenium,rhenium powder or rhenium nanoparticles. The rhenium is preferably addedas rhenium dioxide, rhenium trioxide, rhenium(VII) oxide or ammoniumperrhenate. The rhenium is generally present in a total quantity of atleast 0.01 moles, preferably at least 0.025 moles and more preferably atleast 0.045 moles, and most preferably at least 0.05 moles per mole ofiron oxide calculated as Fe₂O₃. The rhenium is generally present in atotal quantity of at most 1 mole, and preferably at most 0.5 moles permole of iron oxide.

The catalyst may further comprise a lanthanide. The lanthanide isselected from the group of lanthanides of atomic number in the range offrom 57 to 66 inclusive. The lanthanide is preferably cerium. Thelanthanide may be present as a compound of a lanthanide. The lanthanideis generally present in a total quantity of at least 0.02 moles,preferably at least 0.05 moles, more preferably at least 0.06 moles permole of iron oxide, calculated as Fe₂O₃. The lanthanide is generallypresent in a total quantity of at most 0.2 moles, preferably at most0.15 moles, more preferably at most 0.14 moles per mole of iron oxide.The lanthanide compound may include hydroxides; carbonates;bicarbonates; carboxylates, for example, formates, acetates, oxalatesand citrates; nitrates; and oxides. The preferred lanthanide compound iscerium carbonate.

The catalyst may further comprise an alkaline earth metal or compoundthereof. The alkaline earth metal may be calcium or magnesium, and it ispreferably calcium. The alkaline earth metal compound is generallypresent in a quantity of at least 0.01 moles, and preferably at least0.02 moles per mole of iron oxide calculated as Fe₂O₃. The alkalineearth metal compound is generally present in a quantity of at most 1mole, and preferably at most 0.2 moles per mole of iron oxide.

The catalyst may further comprise a Column 6 metal or compound thereof.The Column 6 metal may be molybdenum or tungsten, and it is preferablymolybdenum. The Column 6 metal is generally present in a quantity of atleast 0.01 moles, preferably at least 0.02 moles per mole of iron oxide,calculated as Fe2O3. The Column 6 metal is generally present in aquantity of at most 0.5 moles, preferably at most 0.1 moles per mole ofiron oxide.

The catalyst may further comprise silver or a compound thereof. Thesilver may be present as silver, silver oxide, or silver ferrite. Thesilver is preferably added to the catalyst mixture as silver oxide,silver chromate, silver ferrite, silver nitrate, or silver carbonate.

Additional catalyst components that may be combined with the iron oxideinclude metals and compounds thereof selected from the group consistingof: Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mn, Tc, Ru, Os, Co, Rh, Ir, Ni,Pd, Pt, Cu, Au, Zn, Cd, Hg, Al, Ga, In, Tl, Si, Ge, Sn, Pb, P, As, Sb,Bi, S, Se and Te. These components may be added by any method known tothose skilled in the art. The additional catalyst components may includehydroxides; bicarbonates; carbonates; carboxylates, for exampleformates, acetates, oxalates and citrates; nitrates; and oxides.Palladium, platinum, ruthenium, rhodium, iridium, copper, and chromiumare preferred additional catalyst components.

The catalyst may be prepared by any method known to those skilled in theart. For example, a paste may be formed comprising iron oxide, alkalimetal or a compound thereof, rhenium or a compound thereof and anyadditional catalyst component(s). A mixture of these catalyst componentsmay be mulled and/or kneaded or a homogenous or heterogeneous solutionof any of these components may be impregnated on the iron oxide.Sufficient quantities of each component may be calculated from thecomposition of the catalyst to be prepared. Examples of applicablemethods can be found in U.S. Pat. Nos. 5,668,075; 5,962,757; 5,689,023;5,171,914; 5,190,906, 6,191,065, and EP 1027928, which are hereinincorporated by reference.

In forming the catalyst, a mixture comprising iron oxide, alkali metalor a compound thereof, rhenium or a compound thereof and any additionalcatalyst component(s) may be shaped into pellets of any suitable form,for example, tablets, spheres, pills, saddles, trilobes, twistedtrilobes, tetralobes, rings, stars, hollow and solid cylinders, andasymmetrically lobed particles as described in U.S. Patent ApplicationPublication 2005-0232853. The addition of a suitable quantity of water,for example up to 30 wt %, typically from 2 to 20 wt %, calculated onthe weight of the mixture, may facilitate the shaping into pellets. Ifwater is added, it may be at least partly removed prior to calcination.Suitable shaping methods are pelletizing, extrusion, and pressing.Instead of pelletizing, extrusion or pressing, the mixture may besprayed or spray-dried to form a catalyst. If desired, spray drying maybe extended to include pelletization and calcination.

An additional compound may be combined with the mixture that acts as anaid to the process of shaping and/or extruding the catalyst, for examplea saturated or unsaturated fatty acid (such as palmitic acid, stearicacid, or oleic acid) or a salt thereof, a polysaccharide derived acid ora salt thereof, or graphite, starch, or cellulose. Any salt of a fattyacid or polysaccharide derived acid may be applied, for example anammonium salt or a salt of any metal mentioned hereinbefore. The fattyacid may comprise in its molecular structure from 6 to 30 carbon atoms(inclusive), preferably from 10 to 25 carbon atoms (inclusive). When afatty acid or polysaccharide derived acid is used, it may combine with ametal salt applied in preparing the catalyst, to form a salt of thefatty acid or polysaccharide derived acid. A suitable quantity of theadditional compound is, for example, up to 1 wt %, in particular 0.001to 0.5 wt %, relative to the weight of the mixture.

After formation, the catalyst mixture may be dried and calcined. Dryinggenerally comprises heating the catalyst at a temperature of from about30° C. to about 500° C., preferably from about 100° C. to about 300° C.Drying times are generally from about 2 minutes to 5 hours, preferablyfrom about 5 minutes to about 1 hour. Calcination generally comprisesheating the catalyst, typically in an inert, for example nitrogen orhelium or an oxidizing atmosphere, for example an oxygen containing gas,air, oxygen enriched air or an oxygen/inert gas mixture. The calcinationtemperature is typically at least about 600° C., or preferably at leastabout 700° C., more preferably at least 825° C. The calcinationtemperature will typically be at most about 1600° C., or preferably atmost about 1300° C. Typically, the duration of calcination is from 5minutes to 12 hours, more typically from 10 minutes to 6 hours.

The catalyst formed according to the invention may exhibit a wide rangeof physical properties. The surface structure of the catalyst, typicallyin terms of pore volume, median pore diameter and surface area, may bechosen within wide limits. The surface structure of the catalyst may beinfluenced by the selection of the temperature and time of calcination,and by the application of an extrusion aid.

Suitably, the pore volume of the catalyst is at least 0.01 ml/g, moresuitably at least 0.05 ml/g. Suitably, the pore volume of the catalystis at most 0.5, preferably at most 0.4 ml/g, more preferably at most 0.3ml/g, and most preferably at most 0.2 ml/g. Suitably, the median porediameter of the catalyst is at least 500 Å, in particular at least 1000Å. Suitably, the median pore diameter of the catalyst is at most 20000Å, in particular at most 15000 ∪. In a preferred embodiment, the medianpore diameter is in the range of from 2000 to 10000 Å. As used herein,the pore volumes and median pore diameters are as measured by mercuryintrusion according to ASTM D4282-92, to an absolute pressure of 6000psia (4.2×10⁷ Pa) using a Micromeretics Autopore 9420 model; (130°contact angle, mercury with a surface tension of 0.473 N/m). As usedherein, median pore diameter is defined as the pore diameter at which50% of the mercury intrusion volume is reached.

The surface area of the catalyst is preferably in the range of from 0.01to 20 m²/g, more preferably from 0.1 to 10 m²/g.

The crush strength of the catalyst is suitably at least 10 N/mm, andmore suitably it is in the range of from 20 to 100 N/mm, for exampleabout 55 or 60 N/mm.

In another aspect, the present invention provides a process for thedehydrogenation of a dehydrogenatable hydrocarbon by contacting adehydrogenatable hydrocarbon and steam with an iron oxide based catalystmade according to the invention to produce the correspondingdehydrogenated hydrocarbon.

The dehydrogenated hydrocarbon formed by the dehydrogenation process isa compound having the general formula:

R¹R²C═CH₂

wherein R¹ and R² independently represent an alkyl, alkenyl or a phenylgroup or a hydrogen atom.

The dehydrogenatable hydrocarbon is a compound having the generalformula:

R¹R²HC—CH₃

wherein R¹ and R² independently represent an alkyl, alkenyl or a phenylgroup or a hydrogen atom.

A suitable phenyl group may have one or more methyl groups assubstitutes. A suitable alkyl group generally has from 2 to 20 carbonatoms per molecule, and preferably from 3 to 8 carbon atoms such as inthe case of n-butane and 2-methylbutane. Suitable alkyl substituents arepropyl (—CH₂—CH₂—CH₃), 2-propyl (i.e., 1-methylethyl, —CH(—CH₃)₂), butyl(—CH₂—CH₂—CH₂—CH₃), 2-methyl-propyl (—CH₂—CH(—CH₃)₂), and hexyl(—CH₂—CH₂—CH₂—CH₂—CH₂—CH₃), in particular ethyl (—CH₂—CH₃). A suitablealkenyl group generally has from about 4 to about 20 carbon atoms permolecule, and preferably from 4 to 8 carbon atoms per molecule.

The dehydrogenatable hydrocarbon may be an alkyl substituted benzene,although other aromatic compounds may be applied as well, such as alkylsubstituted naphthalene, anthracene, or pyridine. Examples of suitabledehydrogenatable hydrocarbons are butyl-benzene, hexylbenzene,(2-methylpropyl)benzene, (1-methylethyl)benzene (i.e., cumene),1-ethyl-2-methyl-benzene, 1,4-diethylbenzene, ethylbenzene, 1-butene,2-methylbutane and 3-methyl-1-butene. It is possible to convert n-butanewith the present process via 1-butene into 1,3-butadiene and2-methylbutane via tertiary amylenes into isoprene.

Examples of preferred dehydrogenated hydrocarbons that can be producedby the process are butadiene, alpha methyl styrene, divinylbenzene,isoprene and styrene.

The dehydrogenation process is frequently a gas phase process; wherein agaseous feed comprising the reactants is contacted with the solidcatalyst. The catalyst may be present in the form of a fluidized bed ofcatalyst particles or in the form of a packed bed. The process may becarried out as a batch process or as a continuous process. Hydrogen maybe a further product of the dehydrogenation process, and thedehydrogenation in question may be a non-oxidative dehydrogenation.Examples of applicable methods for carrying out the dehydrogenationprocess can be found in U.S. Pat. Nos. 5,689,023; 5,171,914; 5,190,906;6,191,065, and EP 1027928, which are herein incorporated by reference.

It is advantageous to apply water, which may be in the form of steam, asan additional component of the feed. The presence of water will decreasethe rate of deposition of coke on the catalyst during thedehydrogenation process. Typically the molar ratio of water to thedehydrogenatable hydrocarbon in the feed is in the range of from 1 to50, more typically from 3 to 30, for example from 5 to 10.

The dehydrogenation process is typically carried out at a temperature inthe range of from 500 to 700° C., more typically from 550 to 650° C.,for example 600° C., or 630° C. In one embodiment, the dehydrogenationprocess is carried out isothermally. In other embodiments, thedehydrogenation process is carried out in an adiabatic manner, in whichcase the temperatures mentioned are reactor inlet temperatures, and asthe dehydrogenation progresses the temperature may decrease typically byup to 150° C., more typically by from 10 to 120° C. The absolutepressure is typically in the range of from 10 to 300 kPa, more typicallyfrom 20 to 200 kPa, for example 50 kPa, or 120 kPa.

If desired, one, two, or more reactors, for example three or four, maybe applied. The reactors may be operated in series or parallel. They mayor may not be operated independently from each other, and each reactormay be operated under the same conditions or under different conditions.

When operating the dehydrogenation process as a gas phase process usinga packed bed reactor, the LHSV may preferably be in the range of from0.01 to 10 h⁻¹, more preferably in the range of from 0.1 to 2 h⁻¹. Asused herein, the term “LHSV” means the Liquid Hourly Space Velocity,which is defined as the liquid volumetric flow rate of the hydrocarbonfeed, measured at normal conditions (i.e., 0° C. and 1 bar absolute),divided by the volume of the catalyst bed, or by the total volume of thecatalyst beds if there are two or more catalyst beds.

The conditions of the dehydrogenation process may be selected such thatthe conversion of the dehydrogenatable hydrocarbon is in the range offrom 20 to 100 mole %, preferably from 30 to 80 mole %, or morepreferably from 35 to 75 mole %.

The activity (T70) of the catalyst is defined as the temperature undergiven operating conditions at which the conversion of thedehydrogenatable hydrocarbon in a dehydrogenation process is 70 mole %.A more active catalyst thus has a lower T70 than a less active catalyst.The corresponding selectivity (S70) is defined as the selectivity to thedesired product at the temperature at which conversion is 70 mole %.

The dehydrogenated hydrocarbon may be recovered from the product of thedehydrogenation process by any known means. For example, thedehydrogenation process may include fractional distillation or reactivedistillation. If desirable, the dehydrogenation process may include ahydrogenation step in which at least a portion of the product issubjected to hydrogenation by which at least a portion of any byproductsformed during dehydrogenation, are converted into the dehydrogenatedhydrocarbon. The portion of the product subjected to hydrogenation maybe a portion of the product that is enriched in the byproducts. Suchhydrogenation is known in the art. For example, the methods known fromU.S. Pat. Nos. 5,504,268; 5,156,816; and U.S. Pat. No. 4,822,936, whichare incorporated herein by reference, are readily applicable to thepresent invention.

One preferred embodiment of a dehydrogenation process is thenonoxidative dehydrogenation of ethylbenzene to form styrene. Thisembodiment generally comprises feeding a feed comprising ethylbenzeneand steam to a reaction zone containing catalyst at a temperature offrom about 500° C. to about 700° C. Steam is generally present in thefeed at a steam to hydrocarbon molar ratio of from about 7 to about 15.In the alternative this process may be carried out at a lower steam tohydrocarbon molar ratio of from about 1 to about 7, preferably of fromabout 2 to about 6.

Another preferred embodiment of a dehydrogenation process is theoxidative dehydrogenation of ethylbenzene to form styrene. Thisembodiment generally comprises feeding ethylbenzene and an oxidant, forexample, oxygen, iodide, sulfur, sulfur dioxide, or carbon dioxide to areaction zone containing catalyst at a temperature of from about 500° C.to about 800° C. The oxidative dehydrogenation reaction is exothermic sothe reaction can be carried out at lower temperatures and/or lower steamto oil ratios.

Another preferred embodiment of a dehydrogenation process is thedehydrogenation of isoamylenes to form isoprene. This embodimentgenerally comprises feeding a mixed isoamylene feed comprising2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene into areaction zone containing catalyst at a temperature of from about 525° C.to about 675° C. The process is typically conducted at atmosphericpressure. Steam is generally added to the feed at a steam to hydrocarbonmolar ratio of from about 13.5 to about 31.

Another preferred embodiment of a dehydrogenation process is thedehydrogenation of butene to form butadiene. This embodiment generallycomprises feeding a mixed butylenes feed comprising 1-butene and2-butene (cis and/or trans isomers) to a reaction zone containingcatalyst at a temperature of from about 500° C. to about 700° C.

Due to the endothermic nature of most of these dehydrogenationprocesses, additional heat input is often desirable to maintain therequired temperatures to maintain conversion and selectivity. The heatcan be added before a reaction zone, between reaction zones when thereare two or more zones, or directly to the reaction zone.

A preferred embodiment of a suitable heating method is the use of aconventional heat exchanger. The process stream may be heated beforeentering the first or any subsequent reactors. Preferred sources of heatinclude steam and other heated process streams.

Another preferred embodiment of a suitable heating method is the use ofa flameless distributed combustion heater system as described in U.S.Pat. No. 7,025,940, which is herein incorporated by reference.

Another preferred embodiment of a suitable heating method is catalyticor noncatalytic oxidative reheat. Embodiments of this type of heatingmethod are described in U.S. Pat. Nos. 4,914,249; 4,812,597; and U.S.Pat. No.4,717,779; which are herein incorporated by reference.

The dehydrogenated hydrocarbon produced by the dehydrogenation processmay be used as a monomer in polymerization processes andcopolymerization processes. For example, the styrene obtained may beused in the production of polystyrene and styrene/diene rubbers. Theimproved catalyst performance achieved by this invention with a lowercost catalyst leads to a more attractive process for the production ofthe dehydrogenated hydrocarbon and consequently to a more attractiveprocess which comprises producing the dehydrogenated hydrocarbon and thesubsequent use of the dehydrogenated hydrocarbon in the manufacture ofpolymers and copolymers which comprise monomer units of thedehydrogenated hydrocarbon. For applicable polymerization catalysts,polymerization processes, polymer processing methods and uses of theresulting polymers, reference is made to H. F. Marks, et al. (ed.),“Encyclopedia of Polymer Science and Engineering”, 2^(nd) Edition, NewYork, Volume 16, pp 1-246, and the references cited therein.

The following examples are presented to illustrate the invention, butthey should not be construed as limiting the scope of the invention.Examples 1-7 and Examples 11-15 were conducted in cooperation with hteAktiengesellschaft, Heidelberg, Germany. The other examples wereconducted using standard isothermal testing conditions.

Example 1 (Comparative)

A catalyst was prepared by combining: 13.5 g iron oxide (Fe₂O₃) made byheat decomposition of iron chloride, 1.5 g yellow iron oxide (FeOOH),3.97 g potassium carbonate, 2.07 g cerium carbonate (as hydratedCe₂(CO₃)₃ containing 52 wt % Ce), 0.24 g molybdenum trioxide, and 0.24 gcalcium carbonate. Water was added to the mixture and the mixture wasmulled for 15 minutes. This mixture was extruded to pellets that were 3mm in diameter and about 3 mm in length. The pellets were dried in airat 170° C. for 15 minutes and subsequently calcined in air at 900° C.for 1 hour. The pellets were crushed with a mortar and pestle and sievedwith an appropriate sieve such that the particle size was between315-500 μm.

A 1.1 ml sample of the catalyst was loaded into the isothermal zone of amultiwell reactor (5 mm inner diameter) and was used for the preparationof styrene from ethylbenzene. Inert was loaded above and below thecatalyst bed. The testing conditions were as follows: outlet partialpressure 76 kPa, steam to ethylbenzene molar ratio 10, and LHSV 0.65h⁻¹. In this test, the temperature was initially held at 590° C. for aperiod of about 13 days. The catalyst was then tested for 24 hours ateach of three different temperatures: about 590° C., about 595° C., andabout 600° C. The conversion of ethylbenzene (“C”) and selectivity tostyrene (“S”) at the three temperatures, as measured, is shown inTable 1. This catalyst was tested in duplicate and the data shown is theaverage results.

Examples 2-7

Catalysts were prepared according to the invention. The ingredientsdescribed in Example 1 were used. The catalysts of examples 2-7contained rhenium that was added in different forms and amounts(millimoles of Re per mole of iron oxide, calculated as Fe₂O₃) as shownin Table 1. The catalysts were tested under the same conditions as thecatalyst of Example 1, and the catalyst performance is shown in Table 1.

TABLE 1 Rhenium First Temperature Second Temperature Third TemperatureExample Compound Amount T ° C. C % S % T ° C. C % S % T ° C. C % S % 1(Comp) N/A 0 590 65.6 96.3 595 68.9 95.9 600 72.1 95.6 2 ReO₂ 15 58959.1 97.3 595 62.8 96.9 600 66.3 96.8 3 ReO₃ 15 589 60.4 96.9 594 64.296.6 599 67.6 96.3 4 Re₂O₇ 15 590 64.2 96.6 595 68.1 96.3 601 71.3 95.95 Re₂O₇ 50 590 63.2 96.8 596 67.2 96.4 601 70.6 96.1 6 Re₂O₇ 150 59043.4 97.0 595 49.6 97.1 600 60.5 97.1 7 NH₄ReO₄ 15 590 61.4 96.9 59565.4 96.6 601 69.1 96.3

As can be seen from Examples 1-7, a catalyst containing rhenium is moreselective than a catalyst without rhenium.

Examples 8-10 (Comparative)

Catalysts were prepared by combining: 900 g iron oxide (Fe₂O₃) (made byheat decomposition of iron chloride) that contained 0.08 wt % Cl and hada surface area of 3.2 m²/g and 100 g yellow iron oxide (FeOOH) withsufficient potassium carbonate, cerium carbonate (as hydrated Ce₂(CO₃)₃containing 52 wt % Ce), molybdenum trioxide, and calcium carbonate togive a catalyst with a composition as shown in Table 2. Water (about 10wt %, relative to the weight of the dry mixture) was added to form apaste, and the paste was extruded to form 3 mm diameter cylinders thatwere then cut into 6 mm lengths. The pellets were dried in air at 170°C. for 15 minutes and subsequently calcined in air at 900° C. for 1hour. The composition of the catalyst after calcination is shown inTable 2 as millimoles per mole of iron oxide, calculated as Fe₂O₃. Thecatalysts of Examples 9 and 10 also contained rhenium as shown in Table2.

A 100 cm³ sample of each catalyst was used for the preparation ofstyrene from ethylbenzene under isothermal testing conditions in areactor designed for continuous operation. The conditions were asfollows: absolute pressure 76 kPa, steam to ethylbenzene molar ratio 10,and LHSV 0.65 h⁻¹. In this test, the temperature was initially held at595° C. for a period of about 10 days. The temperature was lateradjusted such that a 70 mole % conversion of ethylbenzene was achieved(T70). The selectivity (S70) to styrene at the selected temperature wasmeasured.

TABLE 2 Composition, millimoles/mole of iron oxide T70 S70 Example Re MoCe Ca K ° C. % 8 (Comp) 0 18 80 25 620 596.1 95.6 9 (Comp) 1.1 (added as18 80 25 620 597.7 95.6 Re₂O₇) 10 (Comp)  7.5 (added as 18 80 25 620595.6 95.4 NH₄ReO₄)

As can be seen from Examples 8-10, small amounts of rhenium added to acatalyst do not improve the selectivity of the catalyst.

Examples 11 (Comparative) and 12-15

Examples 11-15 demonstrate the effects on catalyst performance of addingrhenium and silver to catalysts. These Examples also demonstrate theeffects of changes in calcination temperature and cerium levels. Thesecatalysts were prepared according to the method of Examples 1 except forthe differences in ingredients and the differences in calcinationtemperature, as shown in Table 3. Rhenium was added as Re₂O₇ and silverwas added as Ag₂O. The catalysts were tested under the same conditionsas the catalyst of Example 1 except that the catalyst was broken in for21 days and the conversion and selectivity were measured at about 590°C., about 593° C., and about 596° C. The respective temperatures,conversion (“C”) and selectivity to styrene (“S”) are shown in Table 4.

TABLE 3 Calc. Example K Mo Ca Ce Re Ag T ° C. 11 (Comp) 620 18 25 80 0 0900 12 620 18 25 120 25 200 825 13 620 18 25 120 25 60 975 14 620 18 2580 62.5 130 900 15 620 18 25 120 100 60 825

TABLE 4 First Second Third Temperature Temperature Temperature Example T° C. C % S % T ° C. C % S % T ° C. C % S % 11 (Comp) 591 66.3 96.5 59468.2 96.3 597 70.2 96.1 12 590 70.3 96.1 593 71.8 95.7 596 73.5 95.4 13590 64.3 97.1 593 66.2 96.9 596 68.3 96.8 14 590 66.3 96.9 593 67.9 96.8596 69.8 96.6 15 589 69.3 96.4 592 67.9 96.8 595 72.5 96.0

One skilled in the art can vary many of the variables shown above inaddition to other variables to achieve a dehydrogenation catalyst thatis most effective for a particular application. Additional catalystcomponents may also be added to affect the properties and performance ofthe catalyst. The catalyst manufacturing process may be altered withrespect to such variables as drying times and temperatures, calcinationtimes and temperatures, and processing speed to affect the propertiesand performance of the catalyst.

1. A dehydrogenation catalyst comprising an iron oxide, an alkali metalor compound thereof, and rhenium or a compound thereof wherein therhenium or compound thereof is present in an amount of at least about0.01 moles of rhenium per mole of iron oxide, calculated as Fe₂O₃.
 2. Acatalyst as claimed in claim 1 wherein the rhenium or a compound thereofis present in an amount of from about 0.02 to about 0.5 moles of rheniumper mole of iron oxide, calculated as Fe₂O₃.
 3. A catalyst as claimed inclaim 1 wherein the rhenium or a compound thereof is present in anamount of at most 0.3 moles of rhenium per mole of iron oxide,calculated as Fe₂O₃.
 4. A catalyst as claimed in claim 1 wherein therhenium or a compound thereof is present in an amount of from about 0.04to about 0.25 moles of rhenium per mole of iron oxide, calculated asFe₂O₃.
 5. A catalyst as claimed in claim 1 wherein the alkali metal orcompound thereof comprises potassium.
 6. A catalyst as claimed in claim1 wherein the catalyst further comprises a lanthanide or a compoundthereof.
 7. A catalyst as claimed in claim 6 wherein the lanthanide orcompound thereof comprises cerium.
 8. A catalyst as claimed in claim 1further comprising an alkaline earth metal or compound thereof.
 9. Acatalyst as claimed in claim 8 wherein the alkaline earth metal orcompound thereof comprises calcium.
 10. A catalyst as claimed in claim 1further comprising a Column 6 metal or compound thereof.
 11. A catalystas claimed in claim 10 wherein the Column 6 metal or compound thereofcomprises molybdenum.
 12. A catalyst as claimed in claim 1 wherein thecatalyst further comprises silver or a compound thereof.
 13. A catalystas claimed in claim 1 wherein the catalyst further comprises a metalselected from the group consisting of palladium, platinum, ruthenium,osmium, rhodium, iridium, titanium and copper.
 14. A catalyst as claimedin claim 1 wherein the iron oxide comprises regenerator iron oxideformed by the heat decomposition of an iron halide.
 15. A catalyst asclaimed in claim 1 wherein the iron oxide is restructured byheat-treating in the presence of a restructuring agent.
 16. A processfor preparing a dehydrogenation catalyst comprising preparing a mixtureof an iron oxide, an alkali metal or compound thereof, and rhenium or acompound thereof wherein the rhenium is present in an amount of at leastabout 0.01 moles of rhenium per mole of iron oxide, calculated as Fe₂O₃and calcining the mixture.
 17. A process for preparing a dehydrogenationcatalyst comprising preparing a mixture of iron oxide, an alkali metalor compound thereof, and a rhenium compound selected from the groupconsisting of rhenium dioxide, rhenium trioxide, rhenium(VII) oxide, andammonium perrhenate and calcining the mixture.
 18. A process as claimedin claim 16 further comprising adding an alkaline earth metal orcompound thereof to the mixture.
 19. A process as claimed in claim 16further comprising adding a Column 6 metal or compound thereof to themixture.
 20. A process as claimed in claim 16 wherein the calcining iscarried out at a temperature of from about 600° C. to about 1300° C. 21.A process as claimed in claim 16 wherein the calcining is carried out ata temperature of from about 750° C. to about 1200° C.
 22. A process asclaimed in claim 16 wherein the calcining is carried out at atemperature greater than 800° C.
 23. A process for dehydrogenating adehydrogenatable hydrocarbon comprising contacting a feed comprising adehydrogenatable hydrocarbon with a catalyst comprising an iron oxide,an alkali metal or compound thereof, and rhenium or a compound thereofwherein the rhenium or compound thereof is present in an amount of fromabout 0.015 to about 1 mole of rhenium per mole of iron oxide,calculated as Fe₂O₃.
 24. A process for dehydrogenating adehydrogenatable hydrocarbon comprising contacting a feed comprising adehydrogenatable hydrocarbon with a catalyst prepared from a mixture ofiron oxide, an alkali metal or compound thereof, and a rhenium compoundselected from the group consisting of rhenium dioxide, rhenium trioxide,rhenium(VII) oxide, and ammonium perrhenate.
 25. A process as claimed inclaim 23 wherein the dehydrogenatable hydrocarbon comprisesethylbenzene.
 26. A process as claimed in claim 23 wherein the feedfurther comprises steam.
 27. A process as claimed in claim 26 whereinthe steam is present in the feed at a molar ratio of from 0.5 to 12moles of steam per mole of dehydrogenatable hydrocarbon.
 28. A processas claimed in claim 26 wherein the steam is present in the feed at amolar ratio of from 1 to 6 moles of steam per mole of dehydrogenatablehydrocarbon.
 29. A method of using a dehydrogenated hydrocarbon formaking polymers or copolymers, comprising polymerizing thedehydrogenated hydrocarbon to form a polymer or copolymer comprisingmonomer units derived from the dehydrogenated hydrocarbon, wherein thedehydrogenated hydrocarbon has been prepared in a process for thedehydrogenation of a dehydrogenatable hydrocarbon as claimed in claim23.